The properties of a capacitor are dependent on the voltage applied across the capacitor and/or the current applied through the capacitor, and are particularly dependent on the amplitude, frequency and waveform of these signals. A known technique for measuring a capacitor uses a so-called LCR meter. Used as signal source in an LCR meter is a sine wave.
When a capacitor is used in a circuit, the signals are often not sine waves, but rather block waves or sawtooth, and high currents and/or voltages can occur. Practice has shown that in such conditions an LCR meter does not produce good values for accurate modelling of the capacitor.
WO 2013/110145 discloses a method for calculating model parameters for a coil, comprising of: incorporating the coil into a converter with a switching element; connecting a resistive load; applying an input voltage; controlling the switching element in order to obtain a periodically varying voltage across the coil; measuring at least a first and second quantity representative of respectively the voltage across and the current through the coil; determining at least one voltage value and at least one current value on the basis of the measured first and second quantity; calculating a loss resistance and/or a loss power of the coil on the basis of the at least one voltage value and the at least one current value.
The model that is being used for modelling a coil in WO 2013/110145 comprises a series connection of an inductance L and a loss resistance RLS. Modelling a capacitor is more complex. FIG. 3 of the present application illustrates a possible model for a capacitor comprising a parallel circuit of a loss resistance Rleak and of a series circuit of a capacitance CTEST, a parasitic inductance LESL, a parasitic resistance RESR. Because the parasitic inductance LESL needs to be determined, the skilled person needs to find a way to deal with parasitic inductance in the measurement circuit. This implies that a measurement circuit for modelling coils cannot be simply adapted to be used for modelling capacitors.